1. Field of the Invention
The invention relates to mechanisms for coupling vehicle components such as engines and transaxles to vehicle frames.
2. Description of the Related Art
Conventional lawn vehicles are provided with an engine and other vehicle components that must be supported or coupled with the vehicle frame. A metal or steel vehicle frame is typically utilized, and attachment mechanisms such as bolts are often used for coupling the components to the frame. The metalic frame material is rigid enough to withstand the large compressive force applied by the bolt mechanism.
However, it may be desirable to provide a vehicle having a frame made of a plastic or composite material such that the engine and other vehicle components must be coupled to the plastic frame. These plastic or composite materials will behave elastically within an initial range of stress. If the given stress is high enough, then the plastic material will deform plastically or permanently. Furthermore, plastic or composite materials show properties which are time dependent under load. They can flow under a constantly applied given load (ie. creep) or they can relax under a given deflection (ie. stress relaxation). There are stresses high enough within the elastic range that, when applied to the plastic material over an extended period of time, will cause the material to undergo permanent deflection over time. The load at which the plastic will begin to creep after a period of time is dependent on the particular material used, the time of exposure to the load, the temperature, and other operating conditions. The load at which the plastic will begin to creep after a period of time is dependent on the particular material used, the time of exposure to the load, the temperature, and other operating conditions.
When plastic material is compressed away from conventional bolt connections, the stress within the plastic material may decrease or relax over a period of time if the bolt is not retightened against the plastic. If the bolt connection is retightened against the plastic, then the plastic or composite may continue to flow or creep away from the bolt connection over time.
Since plastic material can be squeezed away from the bolt connection, the thickness of the material can decrease at the location of the bolt. The frame can become weaker as the plastic material continues to flow away from the bolt. The frame may become so weak at the connection point that the frame may fail or the component may break away from the frame.
Many operators do not possess the tools required to measure the torque applied to a bolt. Therefore, a user who has removed a conventional bolt from a plastic frame is capable of applying an amount of torque to the bolt that will cause the plastic to deform non-elastically, or to creep over time.
Therefore, it would be desirable to provide a mechanism for coupling a component to a vehicle having a frame made of a plastic or composite material. It would be desirable for such a mechanism to prevent the plastic material from being compressed into a non-elastic range of stress. Furthermore, it would be desirable for such a mechanism to prevent the plastic material from undergoing stress high enough within the elastic range to cause the material to creep. It would be desirable for the plastic material to remain sufficiently strong to withstand the loads transferred from the component.